1. Field of the Invention
The present invention relates to an apparatus for unloading bulk material from ships in particular, said apparatus comprising a vertical conveyor and a horizontal conveyor connected thereto, said vertical conveyor being provided at its feeding end with a rotary feeding device for feeding the bulk material into the vertical conveyor.
2. The Prior Art
Arrangements of this type have found widespread use in the unloading of especially ships. One example of such an arrangement is described in SE-B-No. 377,099, corresponding to U.S. Pat. No. 3,990,567, according to which the vertical conveyor has a lower feeding device and can be swung outwardly from its vertical position and also raised and lowered, the horizontal conveyor being swingably mounted in such a way that its feeding and cooperating with and connected to the vertical conveyor is raisable and lowerable and also displaceable along a circular arc having its centre at a distance from the feeding end of the horizontal conveyor. In addition, the discharge end of the vertical conveyor and the feeding end of the horizontal conveyor are swingably interconnected, the angle between the two conveyors being controllable by means of a longitudinally controllable device. A development of this arrangement is described in U.S. Pat. No. 4,020,953 in which the vertical and horizontal conveyors are interconnected in a torsionally rigid but pivotal manner for mutual relative movements in a common plane, and furthermore the horizontal conveyor, apart from being swingably connected to the frame or foundation, is tiltably connected thereto for inclination of the plane common to the vertical and horizontal conveyors with respect to a vertical plane.
These prior art arrangements have been equipped with feeding devices according to, for example, U.S. Pat. No. 3,596,751 and have proved to be excellent ship unloaders. The feeding devices serve to promote the feeding of material to the vertical conveyor which frequently is a screw conveyor, the housing and conveyor screw of which are rotatable relative to one another. Usually, the housing is stationary, while the conveyor screw rotates within the housing. Examples of other feeding devices are the device according to European patent publication EP-A-No. 57,167. The devices according to U.S. Pat. No. 3,596,751 and European patent application EP-A-No. 57,167 are of the type where the screw and the feeder are rotated in opposite directions. It thus is the object of the feeder to positively introduce the material into the screw to enable the screw to take an efficient grip on the material and to convey it through the screw conveyor device.
Although the two feeding devices mentioned above by way of example have proved to give a satisfactory supply of material in most cases, they have not always been able to operate efficiently, especially if the vertical conveyor is inclined in relation to the vertical plane or, rather, in relation to the bottom of a ship's hold. Since the unloaders are frequently used for unloading ships, it is necessary to maintain a satisfactory feeding capacity also if the conveyor is inclined to be able to reach into corners and underneath the hatch coaming of the ship's hold. At the same time, it is desired to achieve as complete an unloading as possible also at such not readily accessible locations, thereby to reduce the need for special machines for the cleaning-up of these locations and moving the material within reach of the screw conveyor or the unloader. A further difficulty is that the hold bottom frequently is inclined in relation to the plane in which the frame of the unloading equipment is moving.
It has therefore been proposed to use a control system which, in principle, operates such that, during pendulum movement of the vertical conveyor, an automatic compensation is achieved by raising or lowering the horizontal conveyor, such that the "circular movement" of the feeding device, which is caused by the pendulum movement, will be converted into a rectilinear movement in the horizontal plane. When the tower is rotated, or when the entire unloader is travelling along the ship, no compensation therefore is necessary when the bottom plane of the hold is horizontal or parallel to the plane in which the tower or the entire unloader is moving when travelling along the ship. The problem of compensating for the feeder movement along the bottom of the hold also when the bottom is inclined in relation to the travelling plane of the unloader, has been solved by an invention disclosed in SE-A-No. 8600792-9 which has the same applicant as the present application and according to which the angular position of the feeding device is automatically compensated for during each horizontal movement of the feeding device caused by manual control of the unloader movement, such that the feeding device is made to move in a plane parallel to the bottom plane of the hold.
However, this still leaves the problem that the feeding device does not always take up the best position for efficient cleaning-up and feeding. Thus, it frequently happens that the vertical conveyor is inclined at considerable angles to the vertical plane and to the hold bottom so that the feeder is unable to collect the material and move it into the interior of the feeder and then into the vertical conveyor.
The arrangement according to European patent publication EP-A-No. 57,167 comprises a feeding wing in the form of a helix, for which reason the feeder can operate efficiently only when it is directed exactly perpendicular to the bottom plane of the hold so that the helix will sweep over the hold bottom. The slightest inclination will subject the feeder and the entire unloading equipment to heavy mechanical stresses. The commercially available practical constructions of the feeder according to U.S. Pat. No. 3,596,751 are better in this respect because they function fairly well also when the vertical conveyor is inclined. However, also this type of feeding device tends to leave material and to bump mechanically on the hold bottom when the inclination of the vertical conveyor to the bottom is considerable.
PCT publication WO86/04566 discloses a screw conveyor and a feeding device which are essentially improved in this respect. In this arrangement, the feeder is provided with spokes on which blades are mounted adapted to move the material towards the screw projecting into the feeder, the arrangement being characterised in that the blades have upwardly and downwardly extending portions and are domed like a trawl for drawing the material into the feeder, a lower portion of said blades being arranged to lift the material and move it inwardly towards the feeder, and an upper part of said blades being adapted to draw the material downwards and inwardly towards the interior of the feeder. In its practical constructions, this feeder has three blades which are arranged symmetrically, such that the feeder upon rotation resembles a globe. The globe-like feeder will thus operate in the manner of a milling cutter which efficiently digs into the material, even if this should be densely packed. The difficulty is, however, that the best rpm for tearing loose material is not always the best for feeding the material to the vertical conveyor.
Another problem remaining in prior art feeders therefore is connected with the desideratum that it should be possible to supply the vertical conveyor with bulk materail in as smooth and controlled a flow as possible in order to maintain a high degree of filling in the vertical screw and, thus, a high screw efficiency. It is common practice, in connection with screw conveyors, that the screw is operated at a fixed speed in the range 350-500 rpm, and that one tries to maintain the degree of filling in the screw conveyor at at least 80%, if possible up to 100%, the degree of filling being supervised by measuring the motor current to the driving motor of the vertical conveyor. The degree of filling is controlled by infinitely varying the speed of the feeder, usually in the range 20-60 rpm, in order to compensate for a diminishing degree of filling by increasing the speed, and vice versa. However, this compensation requires access to material within the operating range of the feeder so that the feeder speed need not lie in the upper half of the speed range, which may cause dust problems during unloading of dusty material. In view hereof, the tubular feeder drive shaft surrounding the lower end of the tubular shell of the vertical conveyor is frequently provided with externally mounted tearing means which tear off material from the usually packed material mass in the hold. However, it was found that this tearing and material supply to the feeder is not sufficient under many service conditions. The tearing function frequently necessitates a different speed than the function as a feeder to the feeding end of the vertical conveyor, and it is therefore desired to be able to supply material to the feeding end of the vertical conveyor while utilising a material feeding device whose speed can be controlled with regard to what is required for the actual tearing operation and the feeding of the material and for suppressing unnecessary dust formation during unloading of dusty materials, such as cement. Apart from wanting to suppress unnecessary dust formation, it is also desired, during unloading of dusty materials, to effect separate and controllable tearing also of densely packed material, such as coal, soya meal and tapioca.
A further problem encountered in feeding devices of the type disclosed by European patent publication EP-A-No. 0,057,167 is that such a device gives its best collecting effect if it is operated at low speed, which makes it difficult to satisfy both the tearing function and the function of controlling the degree of filling, and there therefore is need for solving also this problem.